The present invention relates to turbine rotors having integral blade-supporting discs, and particularly to a method for modifying such discs to accommodate a replacement turbine blade requiring a disc having a wider blade supporting area than that required by the original blade.
Certain turbines which are already in service are constructed to have blade supporting discs which are integral with the turbine rotor. In a number of turbines of this type, problems have been encountered with respect to the fastening of some of the blades to their associated discs. One solution to these problems is to replace an existing blade with a new blade which is wider and stronger than the original blade and which requires a disc having a wider blade supporting region.
Conceivably, the necessary modification could be made by cutting off the existing disc as close as possible to its inner extremity and then welding on a new disc. This procedure would be extremely complicated because the disc must be manufactured in two halves in order to be placed around the rotor, and then must be welded to the rotor at a relatively inaccessible location.
A second possibility would involve cutting off the affected rotor end and then welding a new forging in place of the removed portion. This procedure is disadvantageous because such a new forging would be very expensive, given that it would probably include other rows of discs which must be machined and rebladed, certain delays would be encountered in obtaining the new forging, and costly accessory equipment must be obtained for positioning the forging relative the remainder of the rotor during welding.